console.log(a)
var a = 1
console.log(a)
function a() {
  console.log(20)
}
console.log(a)
var a = 3
console.log(a)
function a() {
  console.log(30)
}
a()
console.log(a)

/*
  翻译为:
  -----------------------
  var a
  function a(){console.log(20);}
  function a(){console.log(30);}
  console.log(a);----------------------->[Function: a]
  a=1;
  console.log(a);----------------------->1  
  console.log(a);----------------------->1 
  a=3;  
  console.log(a);----------------------->3  
  a();---------------------------------->此时a=3,报错
  console.log(a);
*/
